Historians will probably never know who first said, "It's Sunday morning. Guess I'll run longer today." Yet for many, "run long Sunday" is carved in stone. Other training tenets offer timeless wisdom ("Don't spit into the wind"), while a few have been mercifully abandoned ("Women shouldn't run more than half a mile"). So how do you tell the good rules from the bad? To find out, we asked six respected, veteran American coaches which commandments they think it's time to stop obeying blindly. You might expect these grizzled sages to be the most faithful to old-time wisdom. But it's precisely their experience that allows them to weigh the pros and cons of precepts that have (or have not) served their runners well. Mind you, the rules they dispute aren't necessarily bad. It's just time to examine whether they're doing you any good. After all, Sunday is a pretty good day for a long run, but if switching to Saturday—or even, God forbid, Monday—helps you squeeze in an extra workout or get an extra day of recovery, that just may be a rule worth breaking.

THE RULE: Stretch before runningBack in the 1970s, Jeff Galloway never worried about stretching. But then experts from other sports began touting the value of "static" stretching—slowly extending muscles—and the idea caught on with runners. "I actually promoted it in my first book," Galloway says now, sheepishly. "Then I got a stream of complaints about injuries it caused." While the link between stretching and injury prevention is still debated, many now believe that static stretching of the legs' springlike muscles and tendons makes them store less energy when you run.HOW TO BREAK IT: Warm up with "dynamic" stretches. Jog for 10 minutes, then do high knees or butt kicks. These moves put muscles through the range of motion that running requires, without the extreme reach-and-hold poses that cause problems.

THE RULE: Do prerace stridesFor generations, runners have followed the same rituals to warm up before races or workouts: Start with some jogging, move on to a little bit of stretching, then perform a series of "strides"—short sprints lasting about 10 seconds that get your heart pumping and kick-start the delivery of oxygen to your running muscles. But do these timeworn rituals really help us perform better? Jack Daniels, Ph.D., isn't convinced. "What I most often see at races is a bunch of runners striding up and down at a speed that is clearly faster than the coming race pace," he says. Since these strides are the last thing runners do before starting the event, that inappropriate pace is fresh in their minds. "And when the gun finally sounds, they 'stride' or sprint right out." The result: a way-too-fast start followed by an inevitable crash.HOW TO BREAK IT: For shorter events like 5-K and 10-K races, jogging just long enough to get a good sweat going is all you need to do, says Daniels. (For longer races, you can get away with even less: Run the first mile of a half or full marathon as your warmup.) To get the oxygen-boosting benefits of strides without skewing your pace judgment—and screwing up your race result—try a sustained two-to three-minute effort 10 minutes before starting the race or workout. Run it slightly faster than your half-marathon pace, or at a speed that feels moderately hard. You should not be sprinting.

THE RULE: Cap your longest run at 20 milesMany marathon-training programs dictate 20 miles for the longest long run. But this leaves runners in uncharted territory for the final 10-K, says Galloway. Based on surveys of thousands of runners, he has concluded that "people 'hit the wall' within about a mile of the length of their longest run." Why? "Part of it's mental," he says. "But at the end of a marathon, guess what? It is mental."HOW TO BREAK IT: If your marathon goal is simply to finish, run up to 26 miles three to four weeks before race day. If you're gunning for a time goal, run up to 29 miles at any pace you can muster. This will help stoke your confidence that you have the endurance to hold your pace right to the end.

THE RULE: Structure your scheduleRunners thrive on routine. But sometimes it pays to schedule workouts based on how you feel, rather than what day it is, says Frank Gagliano. Now that some of his former stars—like 1992 Olympic 5000-meter runner John Trautmann—are in their 40s yet still training hard, "Gags" is making adjustments. "They can't stick to a set weekly schedule—that'll kill them!" he says. Older runners need more time to recover compared with their younger peers (and selves), while runners of any age juggling training, work, and family commitments need to be prepared for—and comfortable with—tweaking their plan.HOW TO BREAK IT: Set up a two-week cycle that includes more downtime. For example, alternate one week that includes two hard runs and one long run with a week that includes a single tough session and a long run.

THE RULE: Push the pace on long runsIt sounds logical: Practice running at goal pace when you're already fatigued from covering a long distance. But it's very difficult for your body to recover after running far and fast, says Galloway.HOW TO BREAK IT: Run long runs at three minutes per mile slower than race pace. This will minimize injury risk and hasten recovery.

THE RULE: Don't bulk upA scrawny upper body is a source of pride for some runners—why carry unnecessary baggage like muscle on your runs? But researchers now realize that sarcopenia—the loss of one to two percent of your muscle mass each year after age 40—is one of the biggest challenges of aging. Strength training helps preserve muscle and strengthen bones (when strong muscles tug on bones, it stimulates new growth), and it's good for your running, too, says Pete Pfitzinger. Studies have found that resistance training can improve your running economy, which reduces the amount of energy it takes to run at a given pace.HOW TO BREAK IT: Do a twice-weekly routine that targets both the upper and lower body, and includes body-weight exercises like push-ups, dips, lunges, and split squats.

THE RULE: Take rest days after long runsSure, rest is the yang to the yin of running, but that doesn't mean you have to take an easy day after every hard day, says Daniels. In fact, muscle soreness often peaks two days after a tough workout, when repairs to microscopic muscle damage hit full throttle. Running back-to-back hard days followed by two consecutive easy days allows your body to fully recover and repair itself.HOW TO BREAK IT: If your long run is on Sunday, schedule fartleks on Monday. Go easy on Tuesday and Wednesday, and do an interval workout or tempo run on Thursday.THE RULE: Cardio cross-trainRoy Benson has nothing against cycling and swimming—he just doesn't think they should be confused with running. "It's called the principle of specificity," he says. "If you want to develop a skill, you need to practice it exclusively." Cross-training builds your aerobic system, but it doesn't develop the muscles and movement patterns necessary for running faster. It may help you avoid injury if you're logging high mileage, but runners with 45 minutes a day or less to train will reap greater benefits by just running.HOW TO BREAK IT: Sub out the XT and run. To avoid injury, tune into your body so that you're running at the appropriate effort level. You don't want to race your easy runs.

THE RULE: Rehab aerobicallyWhen injury strikes, most runners dutifully (if reluctantly) slog away on the elliptical or stationary bike or in the pool to salvage their fitness. When they're cleared to hit the road, they gleefully run for a few days, then BAM!—they're injured again. "All that cross-training built this huge Cadillac engine," Benson says, "but they've got a puny little Chevrolet transmission." The irony is cruel: The aerobic fitness these runners acquire in rehab allows them to start too fast and push too hard when they return to running, compromising the ligaments, tendons, and muscles not yet re-adapted to the stress of running.HOW TO BREAK IT: The real solution, of course, is heeding a superslow return to running. That said, you can minimize the risk posed by an outsized cardiovascular system by spending no more than half of your rehab time on cardio. Spend the remainder on strength and flexibility training to correct muscle imbalances that may have contributed to your injury.

THE RULE: Increase weekly mileage by 10 percentIt's the classic example of commonplace advice calcified into rule. "Sticking to a single number has never made sense to me," says Hal Higdon. Indeed, researchers in the Netherlands found runners following the rule over 13 weeks suffered the same number of injuries as those on a shorter, more aggressive plan.HOW TO BREAK IT: Stay at a given mileage for up to four weeks, then go up. For example, run 20 miles per week for a month, then ramp up to 28 or 30 miles (never go above a 10-mile bump). This gives your body time to adapt so it can work even harder.

THE RULE: Measure your effortHeart-rate monitor, GPS, or even just splits on your Timex Ironman: Many runners are ruled by the numbers on their wrist. "High-tech gadgets are great, but some runners place too much faith in them," Higdon says. The most accurate feedback comes from your own body. Learning how to listen to and interpret that feedback can help you understand where your limits are and how to push them back.HOW TO BREAK IT: Ditch the bells and whistles several times a week. Instead of targeting a specific pace, aim to run easy, medium, or hard and tune into your breathing and stride to ingrain how that effort feels. Or use a GPS to measure your pace, but don't check it until you're finished. Then see if you accurately pegged how you felt to your actual speed.

THE RULE: Wear running shoesHarvard researcher Daniel Lieberman's theory that humans evolved to run long distances suggests that we shouldn't need artificial aid—like running shoes—to log mileage. While the controversy rages on over the role of shoes in injuries, it's clear that adding some barefoot running to your routine can improve your stride, Pfitzinger says. Running sans shoes or in "minimal" models forces the tendons and small stabilizer muscles to work harder, which strengthens your feet and ankles and gradually lengthens your Achilles and calf muscles.HOW TO BREAK IT: Twice a week, ditch your kicks in a grass field. "Start with brisk barefoot walking," Pfitzinger says, "then alternate 30 seconds of running with one minute of walking." Build up over several weeks to five to 10 minutes of continuous running.BOARD OF DETRACTORS

FRANK "GAGS" GAGLIANO74, Rye, New YorkCoaching since 1961. Currently coaches the New Jersey-New York Track Club and is a volunteer coach for Rutgers, the State University of New Jersey.

JEFF GALLOWAY66, AtlantaCoaching since 1978. Competed at the 1972 Olympics in the 10,000 meters; developer of the Galloway Run-Walk-Run Method, a 26.2 plan that emphasizes run/walking.

HAL HIGDON80, Long Beach, IndianaCoaching since 1962. Competed in eight U.S. Olympic Trials, placing as high as fifth in 1960; author of Marathon: The Ultimate Training Guide.

PETE PFITZINGER54, Auckland, New ZealandCoaching since 1979. Top American in two Olympic Marathons (1984, 1988); coauthor of Advanced Marathoning; CEO of the New Zealand Academy of Sport North Island.

The New ResearchRecent studies are forcing us to question additional long-standing advice

Eat breakfast before your run?FRESH TAKE: Sure, being properly fueled helps you run better. And trying to run when your carbohydrate stores are depleted is hard—but not a bad idea if you're looking to shed pounds. Preliminary studies have found running on empty forces your body to burn more fat. But it does take a toll, so do it just a few times a week.

Always race at an even pace?FRESH TAKE: When University of Cape Town scientists analyzed every men's 5000-and 10,000-meter world record set in the modern era, they found the first and last kilometers of the race were faster than any other kilometer for 65 of the 66 records. Similarly, a 2006 study found that running the first mile six percent faster than goal pace led to faster 5-K times than did even pacing.

Push yourself hard up hills?FRESH TAKE: Working hard to maintain your pace when running uphill is a bad strategy, according to Australian researchers. They found the effort of pushing up inclines left study subjects so tired they lost time by running slowly after reaching the top and not going hard enough on the down-hills. Focus on maintaining an even effort rather than an even pace.

Supplement with antioxidants?FRESH TAKE: Vitamin research is a minefield of conflicting findings. Recently, the tide has turned against antioxidant supplements. Large studies have failed to confirm their long-touted age-defying, disease-fighting benefits. Indeed, a few studies now suggest that antioxidants block some of the benefits of training—like improved insulin sensitivity, which helps maintain normal blood-sugar levels—and possibly delay recovery from muscle damage.

Take electrolytes to avoid cramps?FRESH TAKE: Overtraining and poor pacing could be the real culprit. Researchers found that, when compared with noncrampers, runners who cramped up in South Africa's Two Oceans Marathon had run more in the three days prior to the race, had pre-race blood markers indicating damaged or fatigued muscles, and started the event at a more aggressive pace relative to their previous best times.